DIETARY INTAKES AND URINARY-EXCRETION OF CALCIUM AND ACIDS - A CROSS-SECTIONAL STUDY OF WOMEN IN CHINA

The relationship between dietary intakes and urinary calcium was exami ned in a cross-sectional survey of 764 middle-aged and elderly women w ith markedly different dietary patterns and lifestyles. Urinary calciu m was correlated positively with urinary acids, including titratable a cid (r = 0.46, P < 0.0001), ammonia (r = 0.42, P < 0.0001), and sulfat e (r = 0.52, P < 0.0001). Urinary excretions of calcium and acids were correlated positively with intakes of animal and nondairy animal prot ein but were correlated negatively with plant-protein intake, possibly because of the alkaline nature of plant foods. Further analyses showe d that urinary calcium and acids were associated positively with acid- forming foods and were associated negatively with plant foods. These r esults indicate that under free-living conditions urinary calcium excr etion is likely determined by the acid-base status of the total diet, including among other factors the contribution of sulfur amino acids t o urinary acid production.